Abstract
The present work sought to implement a model different from the more traditional ones for the fermentation process of ethanol production by the action of the fungus Saccharomyces cerevisiae, using a relevant metabolic network based on the glycolytic Embden–Meyerhof–Parnas route, also called “EMP”. We developed two models to represent this phenomenon. In the first model, we used the simple and unbranched EMP route, with a constant concentration of microorganisms throughout the process and glucose as the whole substrate. We called this first model “SR”, regarding the Portuguese name “sem ramificações”, which means “no branches”. We developed the second model by simply adding some branches to the SR model. We called this model “CR”, regarding the Portuguese name “com ramificações”, which means “with branches”. Both models were implemented in MATLABTM software considering a constant temperature equal to 32 °C, similar to that practiced in sugar and ethanol plants, and a wide range of substrate concentrations, ranging from 30 to 100 g/L, and all the enzymes necessary for fermentation were already expressed in the cells so all the enzymes showed a constant concentration throughout the fermentation. The addition of common branches to the EMP route resulted in a considerable improvement in the results, especially predicting ethanol production closer to what we saw experimentally. Therefore, the results obtained are promising, making adjustments consistent with experimental data, meaning that all the models proposed here are a good basis for the development of future metabolic models of discontinuous fermentative processes.
Highlights
Accepted: 9 February 2022A wide range of fermented products are still produced by batch or sequential batch processes using accessible raw materials
This point may indicate the need to investigate whether yeast can express different transport proteins at different stages of fermentation, according to the availability of the substrate in the medium: in the present work, the concentrations of relevant enzymes and proteins were constants, since including kinetic expressions for their expression in different phases of the fermentation process is a future step for the development of metabolic models
The present work aimed to propose a model for a batch alcoholic fermentation process using a series of kinetic equations derived from the metabolism of Saccharomyces cerevisiae
Summary
A wide range of fermented products are still produced by batch or sequential batch processes using accessible raw materials. Due to the importance of this type of process, from the second half of the 20th century, a series of works seeking to understand these interactions began to be developed, especially after Gaden [5], who developed an empirical analysis (black box) of batch fermentation processes, verifying whether it was possible to associate the production of a metabolite with cell growth or not. Fermentation processes conducted in batch and fed-batch form generate a considerably complex dynamic interaction between microorganisms and the environment around them, as studied by Freitas et al [10] using genetic algorithms, differential evolution, and real-time dynamic optimization These interactions have been generally studied and well analyzed in the form of black box analyses for some decades, as highlighted by Sainz et al [9], but they fail to consider that each of the cells of a microorganism is capable of carrying out hundreds of reactions simultaneously. In the case of the food industry, this knowledge would make better control of the processes and the selection and development of new strains of microorganisms possible, making it possible to obtain larger amounts of specific substances, especially those involved in aromas and flavors
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